Method and apparatus for humidification of breathable gas by condensation and/or dehumidification

ABSTRACT

A method and apparatus for humidifying breathable gas provided to a user includes providing a breathable gas, producing moisture or water derived from ambient environmental surroundings, e.g., via condensation and/or dehumidified air, and directing the breathable gas along an air flow path. The air flow path optionally includes access to at least a portion of the moisture or water for increased humidification of the breathable gas, for delivery to the user.

CROSS-REFERENCE TO APPLICATION

This application is a divisional of application Ser. No. 11/207,007,filed Aug. 19, 2005, now U.S. Pat. No. 7,525,663 which claims priorityfrom provisional patent application Ser. No. 60/602,872, filed Aug. 20,2004, the entire contents of each of which are incorporated herein byreference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None.

BACKGROUND OF THE INVENTION

Humidifiers are useful to treat a number of ailments that may includenasal dryness and also prevent Rhinitis (inflammation of the nasalmucous membrane). These ailments can be caused by the introduction ofrelatively dry and/or cold breathing gas (e.g. air) to a patient'sairways.

Humidifiers benefit the patient twofold. They add warmth to thebreathing gases, which improves patient breathing comfort and also addsmoisture (e.g. water) to the breathing air to reduce dryness andirritation. Both aspects are especially beneficial during cooler ambientenvironmental conditions such as during cooler seasons (winter).

In the treatment of a patient using ventilation means, thehumidification standard is in the form of an electrical heater thatwarms a body of water which then evaporates the liquid into a vapor orgas that is subsequently introduced to the ventilator's air supply anddelivered to the patient airways.

Other types of humidifiers exist in ventilation and may includenon-heated systems. These may be known as “Passive” or “Passover”humidifiers in the art, however these devices provide limited benefit inefficiency and moisture delivery to the patient airways. Furthermore,there is no warmth being added to the breathing air, which may beirritating should the breathing gas be relatively cool.

There are also air ‘wick’ systems that pass water through moist surfacesor membranes to allow the air to pick up moisture. The moist surfacesgenerally draw water from a water reservoir through a capillary action.As the air passes over the moist surfaces, moisture is picked up and thebreathing gas (air) is delivered to the patient with higher humiditylevels.

Humidifiers currently manufactured for patient ventilation, such asContinuous Positive Airway Pressure (CPAP) used to treat ObstructiveSleep Apnea (OSA), have substantially large water reservoirs (400-600 mlof water capacity). These reservoirs are not user friendly as they needto be filled prior to use, they need to be emptied and cleaned betweenuse, and they are a source of infection as bacteria can accumulate andbe difficult to clean effectively.

Furthermore a patient needs to carry the reservoir to a water source andback to the bedroom after filling, prior to each treatment session. Thisrequires more effort and inconvenience on the user's part.

Current humidification systems aim to generate efficient and high levelsof humidification whilst reducing condensation in the air delivery pathand mask interface. There are numerous systems that have feedback andsensor systems to maximize humidification of the breathing gas or varyhumidification in conjunction with changes in conditions, e.g. ambienttemperature, airflow etc.

Accordingly, a need has developed in the art to address one or moreproblems or shortcomings associated with prior art humidifiers.

BRIEF SUMMARY OF THE INVENTION

One aspect of the invention is to reduce the size of current technology,e.g., by substantially eliminating the water (or fluid) reservoir,and/or improving ease of use by eliminating the need to fill, emptyremains of and/or clean the reservoir.

Another aspect of the invention is to provide a blower with aself-initiating and/or replenishing form of humidification.

These and other aspects will be described in or apparent from thefollowing detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a blower according to an embodiment of thepresent invention;

FIG. 2 is a schematic explanatory view of a Peltier plate that can beused on the blower of FIG. 1;

FIG. 3 is a schematic, cross-sectional, perspective view along line 3-3of FIG. 1;

FIG. 4 is a perspective view of an alternative internal conduitaccording to an embodiment of the present invention;

FIGS. 4A-4B are schematic cross-sectional views of internal conduitsaccording to alternative embodiments of the present invention;

FIG. 5 is a partial perspective and cross-sectional view of a portion ofan internal conduit according to still another embodiment of the presentinvention;

FIG. 6 is a schematic view including the internal conduit portion ofFIG. 5;

FIG. 7 is a partial perspective and cross-sectional view of a portion ofan internal conduit according to another embodiment of the presentinvention;

FIG. 8 is a schematic, cross-sectional view of an internal conduitaccording to still another embodiment of the present invention;

FIG. 9 is a schematic view of a process for use of refrigeration toproduce condensation for use with a blower, according to anotherembodiment of the present invention;

FIG. 10 is a schematic view of a process for use of a freezer pack toproduce condensation for use with a blower, according to yet anotherembodiment of the present invention;

FIG. 11 is a schematic perspective view of a removable drawer for ablower according to still another embodiment of the present invention;

FIG. 12 is a schematic view of a coating, e.g., a spray coating, for usein producing condensation, according to yet another embodiment of thepresent invention;

FIG. 13 is a schematic view of an air delivery tube and patientinterface equipped with a desiccant unit for removal of moisture orwater, according to another embodiment of the present invention; and

FIGS. 14 and 15 are schematic views of a sensor arrangement according toan embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

One embodiment of the invention basically draws its water or moisturefor humidification from the environment (air) surrounding the device.

The atmosphere that humans breathe generally contains some level ofmoisture or humidity in it. The apparatus described herein may use oneor more of the techniques described below to extract this moisture orwater from the air for subsequent use or processing prior to its finaldelivery to a patient's airways, preferably as a humidified breathinggas (above ambient humidity).

In another embodiment, moisture from the atmosphere is condensed onto acooling medium that is in contact with ambient air. One way to createcondensation is to cool the collection surface or surfaces below that ofthe adjacent ambient air (exposed to the collection surface) below theair's Dew Point. Water droplets then condense from the air and onto thecollection surface.

The Dew Point is the temperature at which air must be cooled in order toreach saturation, assuming the air temperature and moisture content areconstant. This saturation results in the liquid (water) condensing fromthe gas (water vapor).

Another embodiment relates to dehumidifying the ambient air, collectingthe water as a liquid and reprocessing this water to increase themoisture content of the breathable gas.

The dehumidified ambient air may also be beneficial in households withexcessive moisture in the room environment, which has benefits ofreducing mold and possibly allergens that may cause asthma attacks, etc.

The chilled surface in contact with the ambient air does not need to bethe actual cooling component of the mechanism. The cooled surface mayalso be created remotely like chillers used in large building coolingsystems. There is a cooling center that subsequently ‘pipes’ the chilledfluid to where it is required.

Dew Point may also be changed by modifying the moisture content ofambient air, for example, using a room humidifier and/or modifying theair temperature.

Cooling may be achieved with several forms of technology from heat pumpsto cold storage devices.

Peltier Heat Pump Methods

FIG. 1 is a schematic diagram of a blower 10 according to an embodimentof the present invention. Blower 10 includes a blower motor 12 thatincludes an inlet for receiving atmospheric gas, e.g., air. Blower motor12 pressurizes the breathable gas to the desired level, e.g., betweenabout 4-20 cm H₂O, for delivery to an air flow path, including aninternal tube 14 within the blower 10. Internal tube 14 delivers thepressurized breathable gas to an outlet 16 provided on an exterior ofthe blower casing. An air delivery conduit 18, also forming part of theair flow path, is provided to the outlet 16, for the delivery ofpressurized breathable gas to a patient interface, such as a mask 20.The breathable gas is transferred from the air flow path to the user'sairways.

Blower includes a control panel 22, which preferably includes a display.Control panel 22 is in communication with a controller 24 to control theoperation of blower 10. Blower motor 12 is also connected to controller24. In addition, controller includes a plurality of inputs 26, 28, forexample, to receive signals from various sensors or transducerstypically provided as part of blower 10. In general, blowers arecommercially available from ResMed, Inc.

Blower 10 includes a humidification unit 30 according to a firstembodiment of the present invention. Generally speaking, humidificationunit 30 has the function of producing moisture or water from ambientenvironmental surroundings. This can help eliminate the need for a bulkyhumidifier unit as is used in the prior art, i.e., the size of thehumidifier can be reduced or the need for a stand-alone humidifier thatrequires water (re-)filling can be virtually eliminated. Of course, thehumidification unit can be embodied as an accessory or after marketdevice. In addition, the humidification unit can be used to(self-)replenish the humidity level of the breathable gas. For example,the blower could be provided with an initial amount (e.g., 100-200 mL)of water, and the humidification unit can produce its own moisture orwater to maintain the desired humidification level, even if the initialwater has been depleted. In this embodiment, humidification unit 30includes a Peltier plate 32 as schematically shown in FIG. 2.Humidification unit 30 is in communication with controller 24.

Peltier plate 32 is similar to Peltier plates used in solid-state heatpumps. In one example of Peltier technology, two insulation layers,e.g., thin ceramic layers 34, 36, sandwich a metal layer, e.g., aBismuth Telluride cube layer 38. As electric current is applied, heat ismoved from one side of the plate to the other; therefore one sidebecomes cold (and produces moisture or water) whilst the other sidebecomes hot. Any other form of thermoelectric heat pump may be used.

FIG. 3 is a perspective, schematic and partial cross-sectional view ofblower 10 in which Peltier plate 32 is provided within blower casing.Blower casing may include at least one vent 40 having one or moreopenings 42. In this example, heat is transferred from ceramic layer 36to ceramic layer 34 such that ceramic layer 36, which is providedadjacent vent 40, begins to collect water droplets 44. Droplets 44descend by gravity along the surface of ceramic layer 36 and aredeposited into an opening 46 provided in internal conduit 14. Layer 36may also be a porous medium that increases the surface area. Some or allof the air may be passed along the surface to increase humidification.Internal conduit 14 may include a reservoir 48 to collect accumulateddroplets once they are received with opening 46. A level detector may beprovided to determine whether the level with receptacle 48 reaches apredetermined maximum limit, at which point the Peltier plate 32 wouldbe switched off or reduced in order to cease production of waterdroplets and condensation.

FIG. 4 illustrates an isometric view showing a portion of internalconduit 14 along with reservoir 48. As shown, reservoir 48 extends alongonly a portion of the extent of conduit 14. However, the length ofreservoir can be changed depending on the desired condensation capacityand/or the size of the Peltier plate 32. Moreover, the length of conduit14 can be changed to allow for an increase or decrease in the size ofthe reservoir and/or the size of the Peltier plate. In one embodiment,the conduit 14 may have a series of bends (with respective reservoirs ora common reservoir) to effectively increase the length. The reservoirmay have a capacity that is very small or negligible, e.g., 10-20 mL orless. If this volume is spread over a sufficiently large surface area,which is preferably very shallow or film-like, it can be heated fromwater or liquid to gas vapor prior to introduction to breathing gas.

FIG. 4A is a schematic cross-sectional view according to anotherembodiment of the present invention. In FIG. 4A, conduit 14 includes aPeltier plate 32 provided to the bottom of reservoir 48. Layer 36 formsa lower surface of the reservoir 48. The polarity of the currentintroduced into plate 32 can be reversed, such that plate 36 can eitherproduce condensation, to add humidification, or heat the reservoir 48,to heat the air and/or evaporate any collected condensation. In oneembodiment, controller 24 (FIG. 1) can cycle plate 32 to eliminate anycollected moisture/water in reservoir at the end of a treatment session,e.g., by using layer 36 in a heating mode to convert the water into gasvapor that may be reintroduced in the breathing gas as humidifiedair/gas. In addition, controller 24 can cycle plate 32 to beginproduction of water or moisture at some predetermined time before thetreatment session begins.

In yet another embodiment, the conduit need not include a reservoir, ifthe amount of water/moisture/condensation produced is approximatelyequal to the amount of humidity to be added to the air flow path. In oneexample shown in FIG. 4B, the conduit 14 may be provided with aplurality of axially and/or circumferentially spaced humidificationunits 30.1-30.7 that can be individually controlled to produce thedesired humidification without the need to collect water or provide areservoir.

For Peltier plates to function efficiently, the ‘waste’ heat needs to beremoved from the hot side. In the application of a patient ventilationdevice, the heat could be removed by the incoming breathable gas, whichmay improve comfort of breathing especially in cooler climates. As shownin FIG. 3, “hot” ceramic layer 34 may be in close proximity to the outersurface of internal conduit 14 to heat the pressurized gas. Layer 34 mayinclude an extension 34 a to heat a further extent of conduit 14, ifdesired. Extension 34 a may be independently operable, to thereby changethe temperature of the heated gas.

The ‘waste’ heat may also be partly or fully utilized to re-evaporatethe condensed water from the cool side of the Peltier plate. Theevaporation of the liquid water into water vapor therefore provides amethod of humidification for the breathable gas.

In another embodiment, the cool side may only be exposed to the ambientair outside of the breathable gas air path. This prevents the breathablegas from being cooled if so desired. In the case of ventilation, warmerbreathing air is more comfortable to the airways. The hotter side of thePeltier plate may be exposed to the breathable gas path so as to heatthe breathing gas. The water condensed from the cool side can then betransferred or otherwise run-off onto the hot side in the breathable gaspath, which results in the breathable gas being heated and humidified.The system would allow only heating, or heating and humidification.

In this application of the Peltier technology, the moisture fromcondensation is insulated from the core of the Peltier plate, asmoisture will have an adverse effect on the life.

A Peltier plate is currently the preferred embodiment of the inventiondue to no noise, no vibration, no moving parts, long life, no FREON(trademark) type refrigerant, compact size, and capable of precisiontemperature control.

Two or more Peltier plates may also be stacked upon one another toachieve higher performance; that is greater cooling and/or heating. Forexample, a second metal layer similar to layer 38 could be provided tothe left side of layer 34 in FIG. 3, and an additional ceramic layerprovided to the second metal layer.

FIG. 5 illustrates a Peltier plate assembly according to yet anotherembodiment of the present invention. In FIG. 5, Peltier plate assembly50 takes the form of a conduit including ceramic layers 34 and 36 andmetal layer 38. Peltier plate assembly 50 may form at least a portion ofinternal conduit 14, as shown in FIG. 6. As shown in FIG. 6, Peltierplate assembly 50 has a diameter which is larger than the diameter ofthe remainder of internal conduit 14. Accordingly, the water level 52which is shown in dotted lines in FIG. 6 can be maintained below thelevel of conduit 14, so as to maintain the condensed moisture within theconduit portion.

FIGS. 7 and 8 illustrate further Peltier plate assemblies according tothe present invention. As shown in FIG. 7, conduit portion 60 is formedsuch that ceramic layer 34 only covers a portion of the circumference ofconduit 60. The conduit per se in FIGS. 5 and 7, which is used to conveypressure as gas and store condensed fluid, may be formed of a ceramicmaterial. Alternatively, a standard plastic conduit may be insertedwithin conduit portion 60. Stated differently, the conduit portion 60could form a sleeve that could be retrofit onto a portion of a conduitof a prior art blower.

In FIG. 8, conduit member 70 includes an inner surface 72 which ispartially defined by plastic portion 74 and partially defined by ceramiclayer 36. Metal layer 38 is provided between ceramic layers 34, 36. Whena DC current is applied, heat may be transferred from layer 36 to layer34, which produces condensation on layer 36, in order to humidify theair. In addition, layer 34 is in contact with plastic portion 74 so asto allow the possibility of heating the air to a desired temperaturelevel. As schematically illustrated in FIG. 8, the lower portion 76 oflayer 34 may be controlled independently of the upper layer 78 of layer34, so as to control the humidity level independently of the heatinglevel.

The Peltier plate, in any embodiment described herein, may also havereversible current to potentially cool air that has become too hot orotherwise to control level of humidity. In the case of humidity, thePeltier plate may re-condense the humidified breathable gas ifhumidification levels were deemed too high.

The Peltier system (or any system described herein) may also havevariable current that allows the level of humidification to be variableor have multiple phasing in/out so that humidification may be profiledaccording to requirements. Attention is directed to U.S. ProvisionalPatent Application No. 60/599,864, filed on Aug. 10, 2004, entitled“Method and Apparatus for Humidification of Breathable Gas With ProfiledDelivery,” incorporated herein by reference in its entirety.

It can be observed that water can condense on a cool surface especiallywhen the cool surface is brought into a warmer environment. Anotherembodiment of the invention is known as a pulsed Peltier effect. It hasthe ability to quickly create condensation on the surface of the coolside of the Peltier plate. Should the DC current to the Peltier plate bereversed, to now warm the same surface, this can encourage fastercondensation should the treatment system require it.

Refrigeration Methods

Refrigeration systems evaporate fluorocarbons suchas FREON (trademark),e.g., using a hot coil (condenser coils) and a cold coil (evaporatorcoils). The cold coil condenses the water whilst the hot coil is exposedto breathing gas to warm air for comfort. The condensed water from thecold side is introduced into the warm breathing gas or hot coil side. Asshown in the example of FIG. 9, a hot coil 80 is provided to the inletof blower motor 12, which then provides the gas to conduit 14. Conduit14 is in communication to receive condensation from cold coil 82, whichallows humidified gas to be provided to the patient via tube 18. Thesystems range in size with compressors about the size of a soccer ballin a typical domestic fridge to miniature sizes approximately fits thepalm of one's hand. The miniature refrigeration systems have been usedin armed forces apparel in arid conditions where the system is used tocool the wearer.

Miniature refrigeration systems are well known devices, for example forcooling food. These refrigeration systems re-evaporate the condensedwater that is considered waste. In the case of the invention, the wateris collected for processing and subsequently used in humidification of abreathing gas.

The same embodiments mentioned under “Peltier Methods” (above) may alsobe applied to refrigeration as it also has a combination of a hotsurface and cold surface, more specifically a hot coil and cold coil.

The refrigeration pump may use “Inverter” type technology where thespeed of the pump can be varied to control cooling/heating efficiency,rather than switching on and off to control output/temperature.

The refrigeration pump, like the Peltier technology can be reverse-cycle(change-over), where the heating coil becomes the cold one and thecooling coil becomes the hot one.

Those embodiments of the invention that have cold and hot elements inthe same system (Refrigeration and Peltier) can also condense themoisture from the cold coil and the dehumidified air may be passed backthrough to offer greater comfort of warm breathing air. The level ofhumidification may be adjusted manually, semi, or fully automated bymodifying the level of moisture being re-evaporated or vaporized intothe breathing gas.

Freezer Pack Embodiments

Another embodiment includes the use of a freezer pack. The pack couldeliminate need to clean or replenish a reservoir. An ice pack, powder,gel, or other method of storing cold or frozen material may be used. Thefreezer pack in one aspect may be frozen in the fridge then taken outand placed into the treatment device. The condensation from the freezerpack is subsequently heated and re-evaporated before administering intothe breathable gas. If so desired, the device may not reheat the air,but simply pass the ambient air over the condensation-covered ice packto raise humidity and cool the air, possibly desirable in hot climates.This is schematically illustrated in FIG. 10, in which freezer pack 86is provided upstream of blower motor 12. Of course, freezer pack may beprovided along any portion of the air delivery path.

The freezer pack, in a preferred embodiment, is a sealed bag or bladderthat can conveniently contain the cold packing material, e.g., water.The bag may be in a shape that occupies a desired space with the mostcompact dimensions. As shown in FIG. 11, freezer pack 86 may bedelivered/removed using an insert member 88, e.g., a slidable drawer orshelf, that can be removed or slid open to expose the inside of blower10. Insert member 88 includes an opening 90 in communication with anopening in conduit 14 to allow for collected moisture to be delivered toconduit 14.

The freezer pack may also be used in conjunction with any form of devicethat may elevate the surrounding temperature (of the freezer pack) toincrease the rate of condensation. An example of this is taking a can ofcold drink out of the fridge and placing it in a warm room. The sides ofthe can exhibit dripping moisture as condensation.

The water collected may either be directly humidified or otherwise endup in a reservoir for subsequent use, for example conventional heatedhumidification.

Cold material may also be contained in a holding body without the use ofa bag, bladder or wrapper. For example, it may be in the form of coldstorage medium that is semi-solid liquid or gel, similar to cold packsused in cosmetics around the eyes.

The material that may be cooled could include any or a combination ofliquid, gas, powder, granule, fluid, viscous fluid such as gel, solidparticles or a solid that is a pre-shaped mass.

Other Embodiments

In the case of CPAP therapy where the flow generator device is generallyonly used at night-time, the device according to the invention may bedesigned to be relatively low in power and less efficient than otherembodiments mentioned (and potentially smaller capacity and sizerequirements). For example, it may collect about 0.5 liters of waterinto a reservoir over a period of say 10-15 hours (sleep is around 8hours). Another embodiment of the invention allows the device to collectwater from the atmosphere during the daytime while the patient is notbeing treated, and by night-time, the device has accumulated enoughcondensed water in a reservoir (essentially a self-filling reservoir),and therefore behave like conventional humidifier systems (with areservoir and heating plate) at the time CPAP therapy begins. It mayhave an automated switch off device once the reservoir is filled tomaximum.

With reference to the embodiment above, the device may also be acombination of a low-power heat pump and a reservoir that is heated.This allows the unit to switch from heat pump tohumidification-efficient heated reservoir as required by the patient. Inthis scenario, the reservoir size may be substantially reduced in size.The switchover between modes may be incremental and concurrent,otherwise may completely switch completely from one to the other.

The unit may have an additional reservoir of water to compensate fordryer periods during a treatment session and also be used to assist withcooling the hot side of coil (refrigeration or Peltier) for greatercooling efficiency. The small reservoir may also provide an additionalhumidification source if insufficient moisture is temporarilyunavailable in the atmosphere.

The device may only condense water but not heat (similar to passive orPassover humidifiers). Humid cool air is perceived warmer and morecomfortable than dry cool air. The dry cool air tends to cool morebecause there is a higher rate of evaporation. This option may bedesirable where only relatively small levels of humidification arerequired.

Water may move over mesh device to increase surface contact with air toimprove efficiency moisture take-up of the air.

Device may be located at the inlet of the gas delivery device (CPAP) orbetween the gas delivery device and the patient interface.

Device may utilize a typical air conditioner used to cool or heat theroom. The drain for the air conditioner's condensate may also beconnected to the humidifying device that introduces the moisture to thebreathing air.

An anti-microbial filter or other barrier may be incorporated into thesystem to prevent bacteria in the moist paths from entering thebreathable gas.

The invention may also be used with or without a ventilator device, maybe a stand-alone unit to administer vaporized gas.

The invention in one preferred embodiment may cycle between switch onand off during the course of the night. These cycles can be regular,irregular, or otherwise controlled for numerous intervals and variousdurations using some smart electronic control. The switching off doesnot necessarily need to completely switch off, but may reduce intemperature during periods where less humidification is required. Asmentioned, this reduces water usage.

The device (invention) may also measure room temperature, humidity orboth as well as monitoring the breathing gas to be delivered to thepatient and optimize setting to produce a desired humidificationprofile. For example, constant level or variable over the course of thetreatment session (night). These sensors may be integral with the deviceor otherwise remote with wired and/or wireless “Blue tooth”communication.

Freezing Gas

A freezing gas may also be used to reduce the temperature of the airbelow the Dew Point. For example, as shown in FIG. 12, a freezingaerosol 92 may be sprayed onto a surface, e.g., a conduit 94 formingpart of the air delivery path, in contact with ambient air. Freezingaerosols are commonly used in electronics had traditionally beenhalogenated CFC (Chlorofluorocarbon). More environmentally friendlysubstances can now be used, such as Hydrofluorocarbons HFC 134 a and HFC152 a. These gases are also used in refrigeration systems quoted above.Any freezing gas that can reduce the air below its Dew Point may beused. For example, Liquid Nitrogen.

Phase Change Materials

A phase change material (PCM) may also be used in further embodiments.PCMs can be described as materials that can change in physical form. Forexample, from solid to liquid, and from liquid to gas as temperaturechanges.

During a phase change from solid to liquid and liquid to gas, heat isabsorbed from the surrounding environment. An example is paraffin wax.Conversely, in cooling from a gas to liquid and liquid to solid, heatcan be given off to the environment. The energy that can be stored orreleased is known as latent heat, and in PCM, occurs over a narrow rangeof temperature. During the change in physical state, the material tendsto remain at relatively constant temperature until phase change iscomplete. The transfer of the latent heat to surroundings produces abroad plateau of near constant temperature.

An embodiment includes the use of a PCM to cool a surface. Furthermore,the near constant temperature characteristics explained earlier, may beutilized with any other form of cooling or heating process to assist inmaintaining temperatures with less fluctuations. This in turn mayprovide more constant temperature control if so desired. For example, aPCM may be used in conjunction with the refrigeration example explainedearlier.

The PCM may be in many forms. Paraffin wax is one example. It may alsobe in the form of eutectic salts or otherwise be in a number of formsincluding liquid, gel, powder, paste or granule, or blended into part ofanother solid. For example placing granules into a thermosettingmaterial.

Moisture Absorbent Materials

Further embodiments to the invention may also use moisture absorbentmaterials such as Silica Gel, typically found in crystalline form. Thissubstance is widely used to absorb atmospheric moisture. The moisture orwater vapor trapped in these crystals may subsequently be harnessed tore-vaporize into the breathing gas, for example by heating.

Silica Gel is one substance that absorbs atmospheric moisture relativelyefficiently. The invention is not limited to the type of substance usedand in general terms, this embodiment relies on the use of a desiccantmaterial. Silica Gel is basically a substance with millions of tinypores that can trap moisture.

Desiccants

A further embodiment uses the desiccant to control the level ofcondensation that occurs. For example, excessive condensation may becontrolled by using Silica gel to absorb some of the excess moisture.

For example, as shown in FIG. 13, a desiccant unit 96 (including adesiccant) may also be applied to the breathing tube 18 to assist inprevention of water droplets in the tube. Desiccant can alternatively beprovided within a unit 98 provided on patient interface 20. Thiscondensation in the breathing tube can cause irritation if a patientinadvertently inhales it.

Embodiments of the invention may also incorporate a switch or sensordevice that switches off the humidifier should the treatment session beinterrupted. For example, an OSA patient may get up in the middle of thenight to go to the bathroom. This feature is designed to reduce waterconsumption further and also prevent condensation in the air deliverypipe, especially if the flow generator has stopped. The flow generatorcan be stopped or started by sensing flow/pressure in the air path,e.g., when the patient dons or removes the mask, to thereby create asignal to activate or deactivate the blower. Such technology isincorporated, e.g., in ResMed's SMARTSTART (trademark) with smart stopand/or smart start feature. It may also prevent the patient breathing incondensate when they return to bed, which in turn improves patientcomfort.

Condensation Moisture Sensor

As shown in FIGS. 14 and 15, one embodiment of the invention may includea humidity or condensation sensor 100 to determine if adequate level ofcondensation, or too much condensation, is occurring. A mask “rain-out”sensor according to an embodiment does not require the use of humiditysensor like the prior art. As schematically shown in FIG. 14, aninfrared emitter 102 and detector 104 are placed, e.g., in side-by-siderelation, at the bottom of the mask interface or location or surface 106where condensation is likely to bead or pool. The mask frame wall infront of the side-by-side emitter/detector is transparent to infraredlight. Under normal conditions, where no condensation or water dropletshave developed (FIG. 14), the detector 104 does not detect any infraredlight. If significant water droplets 108 develop in front of theemitter/detector (FIG. 15), the droplets (condensation) cause theincident light to scatter in most if not all directions, a portion ofwhich scattered light is reflected back to the detector to therebysignify the presence of condensation. Sensor elements, e.g., emitter anddetector, are controlled by appropriate logic, or signals from thedetector/emitter are provided to a processor or computer. The sensor mayalso use another type of visible or non-visible light emitter/detectorcombination.

In another alternative, emitter and detector may be positioned onopposite sides of the location 106. If the light from emitter passesthrough location 106, and is received by detector 104 at full intensity,then it is judged that no condensation is present. If water droplets(condensation) appears, then the emitted light is reflected and/orscattered such that the detector only receives less than the fullintensity of the light, e.g., 50-95%. Therefore, it is judged thatcondensation is present.

A controller 107 associated with the detector would preferably becalibrated or set such that it can distinguish between full intensitylight (no condensation) and less than full intensity light(condensation). The controller may produce a positive or negativecondensation signal depending on whether the detector produces a sensedlight intensity signal that is equal to or greater than a predeterminedfull intensity signal. The sensed intensity of the light changesdepending on whether condensation is causing the light toreflect/scatter.

The emitter/detector above may also be used to sense the level of liquidwhere a reservoir is used.

The above described embodiments may realize one or more of the followingadvantages:

-   -   A humidifier that does not need to be manually filled with water        by a user.    -   Because there is a smaller reservoir or no reservoir, there is        less spilt water.    -   Because the humidification unit is self-initiating, there is not        need for continuous top ups.    -   Water volume requires no consideration. Only requirement is to        set humidification level required.    -   Major benefit over current technologies that does not require a        user to manually fill a reservoir.

While the invention has been described in connection with what arepresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the invention. In addition, while the invention has particularapplication to patients who suffer from OSA, it is to be appreciatedthat patients who suffer from other illnesses (e.g., congestive heartfailure, diabetes, morbid obesity, stroke, barriatric surgery, etc.) canderive benefit from the above teachings. Moreover, the above teachingshave applicability to ventilators in general for use with patients andnon-patients alike.

The invention claimed is:
 1. A method for humidifying breathable gaspressurized by a blower and subsequently provided to a user's airways,the method comprising: producing moisture or water derived from ambientenvironmental surroundings by applying a current to a Peltier plateassembly to create condensation; and channeling the pressurizedbreathable gas from the blower along an air flow path, said flow pathincluding access to at least a portion of the moisture or water producedby the Peltier plate assembly for increased humidification of thepressurized breathable gas, for delivery to the airways of the user. 2.The method according to claim 1, wherein the current within the Peltierplate assembly is reversible.
 3. The method according to claim 1,wherein the moisture or water is directed to a conduit provided as partof the air flow path.
 4. The method according to claim 1, wherein thebreathable gas is positively pressurized to a predetermined level, andthe producing includes heating the breathable gas prior to pressurizingand adding the moisture or water to the air flow path after thepressurizing.
 5. The method according to claim 1, further comprisingheating the breathable gas along at least a portion of the air flow pathto increase the temperature of the breathable gas.
 6. The methodaccording to claim 5, wherein heating of the portion of the air flowpath is controlled independently of the amount of moisture or waterproduced from the ambient environmental surroundings.
 7. The methodaccording to claim 1, wherein the ambient environmental surroundingsinclude ambient air.
 8. The method according to claim 7, wherein theambient air is provided with one or more treatment gasses.
 9. The methodaccording to claim 1, wherein the breathable gas is pressurized within apredetermined positive pressure range.
 10. A blower constructed andconfigured to carry out the method according to claim
 1. 11. The methodaccording to claim 1, wherein a reservoir for collecting producedmoisture or water is provided proximate to the Peltier plate assembly.12. The method according to claim 11, further comprising temporarilydeactivating the Peltier plate assembly when moisture or water in thereservoir exceeds a predetermined limit.
 13. The method according toclaim 1, wherein the breathable gas is pressurized to a level betweenabout 4-20 cm H₂O.
 14. The method according to claim 13, wherein thepressurized breathable gas is provided to the users to achieve acontinuous positive airway pressure and treat the user's sleep disorder.15. A method for humidifying breathable gas pressurized by a blower andsubsequently provided to a user's airways, the method comprising:producing moisture or water derived from ambient environmentalsurroundings; and channeling the pressurized breathable gas from theblower along an air flow path, said flow path including access to atleast a portion of the produced moisture or water for increasedhumidification of the pressurized breathable gas, for delivery to theairways of the user, wherein the producing includes: providing amoisture absorbent material to dehumidify the ambient environmentalsurroundings and create condensation; collecting moisture or waterproduced by the moisture absorbent material; and introducing saidmoisture or water into the air flow path.
 16. A blower constructed andconfigured to carry out the method according to claim
 15. 17. The methodaccording to claim 15, wherein the breathable gas is pressurized to alevel between about 4-20 cm H₂O.
 18. The method according to claim 17,wherein the pressurized breathable gas is provided to the user in toachieve a continuous positive airway pressure and treat the user's sleepdisorder.
 19. A method for humidifying breathable gas pressurized by ablower and subsequently provided to a user's airways, the methodcomprising: producing, in the form of condensation, moisture or waterderived from ambient environmental surroundings; channeling thepressurized breathable gas from the blower along an air flow path, saidflow path including access to at least a portion of the moisture orwater produced by a Peltier plate assembly for increased humidificationof the pressurized breathable gas, for delivery to the airways of theuser; and controlling the amount of said moisture or water produced. 20.The method according to claim 19, wherein said controlling includesheating a portion of the air flow path to evaporate at least a portionof said moisture or water.
 21. The method according to claim 19, whereinsaid controlling includes providing a desiccant unit with a containeddesiccant along a portion of the air flow path.
 22. A blower constructedand configured to carry out the method according to claim
 19. 23. Themethod according to claim 19, wherein a reservoir for collectingproduced moisture or water is provided.
 24. The method according toclaim 23, wherein the controlling includes temporarily suspendingproduction of moisture or water when moisture or water in the reservoirexceeds a predetermined limit.
 25. The method according to claim 19,wherein the breathable gas is pressurized to a level between about 4-20cm H₂O.
 26. The method according to claim 25, wherein the pressurizedbreathable gas is provided to the user in to achieve a continuouspositive airway pressure and treat the user's sleep disorder.